Top Voted Answer

The place ya musta been referring to is Mermaid Gorge or somethin, (the room that has a large swimming pool) there is a box up there that you reach in the next room by going through a hole above a palm tree. The other two not-so-obvious treasures around there are one behind a breakable rock in that room that has lots of breakable rocks, and the one in mermaid gorge that you swim to by going through a small hole somewhere around the edge of the water.

The treasures in rainbow falls are obvious, so that can't be what you meant to ask.

Answers

Old question, but OK. The above poster is wrong. That's an area that is not meant for Terra. I actually managed to get up there by using Aerial Slam against one of those flying yellow lightning guys. Each time you reach a new platform, it will fly back up to get to you, where you can then Slam it again to go higher. (Provided you have little enough strength that it will survive many hits. I was only Level 12, thanks to Zero EXP ability)

Very frustrating to achieve since you can barely reach each cliff, and you have to wait until it feels like moving to the correct spot against the wall in front of you, but all I got for the effort was the usual saying, "There's nothing down this way."